Previous systems for the preparation of such fluids normally operate beginning with one or more liquid based concentrates. For example, U.S. Pat. No. 4,158,034 describes how a concentrate in liquid form is mixed with water for the preparation of a dialysis fluid. In European Patent No. EP-B1-0 22 922, and in U.S. Pat. No. 4,783,273, there is a description of how two liquid-based concentrates can be mixed with water to obtain a fluid intended for medical use, such as a a dialysis fluid. More recently, systems have been introduced which instead make use of one or more concentrates in powder form. For example, U.S. Pat. No. 4,784,495 describes how one or more such powder-based concentrates can be used, with or without the addition of a liquid-based concentrate.
Should one wish to utilize a powder-based concentrate which is difficult to dissolve, it can become quite difficult to achieve acceptably rapid dissolution such as by using the system disclosed in the above-mentioned U.S. Pat. No. 4,784,495. Furthermore, the system according to this patent can become relatively complicated if it is desired to add several different individual pre-packed powder-based concentrates.